The present invention relates to a novel and improved pressure-sensitive resistor or a pressure-sensitive rheostat.
In the prior art, pressure-sensitive resistor elements of a type is widely known and employed which are composite materials composed of an electrically insulating rubbery elastomer as a matrix and an electroconductive particulate material such as carbon black and metal powders dispersed uniformly in the matrix to form an electroconductive rubbery elastomer to be placed between two opposite electrodes. Such an element is used in a pressure-sensitive resistor since the resistance between the electrodes is varied in accordance with the compressive force applied between the electrodes.
The pressure-sensitive resistor of the above described type has the working point in the region of negative coefficient, i.e. in the region where the resistance between the electrodes is decreased as the compressive force applied between the electrodes is increased. Generally speaking, the gradient of the compressive force vs. resistance characteristic curve is considerably large in the region of negative coefficient so that, in other words, the value of the resistance is varied remarkably even with a slight change in the compressive force. Therefore, although the pressure-sensitive resistor of this type is suitably employed in an electric circuit, for example, to give a threshold resistance to control an on-off switching device, it is inapplicable in the fields where it is essential to obtain a delicate control in the value of variable resistance with high reliability.
In addition, the resistance between the electrodes in these pressure-sensitive resistors is a summation of the resistance of the electroconductive resistor element per se and the contact resistance between the electrodes and the electroconductive rubbery elastomer whereas the above mentioned contact resistance in the known electroconductive rubbery elastomer fluctuates irregularly or uncontrollably in accordance with the indefinable contacting condition between the electrode and the electroconductive rubbery elastomer. What is worse, the proportion of the above mentioned contact resistance to the overall resistance is so large that the value of the variable resistance obtained with such a pressure-sensitive resistor is rather poor in reliability and reproducibility.